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1 | =head1 NAME |
2 | |
3 | version - Perl extension for Version Objects |
4 | |
5 | =head1 SYNOPSIS |
6 | |
7 | use version; |
8 | $version = version->new("12.2.1"); # must be quoted for Perl < 5.8.1 |
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9 | print $version; # v12.2.1 |
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10 | print $version->numify; # 12.002001 |
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11 | if ( $version gt "12.2" ) # true |
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12 | |
13 | $alphaver = version->new("1.02_03"); # must be quoted! |
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14 | print $alphaver; # 1.02_0300 |
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15 | print $alphaver->is_alpha(); # true |
16 | |
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17 | $ver = qv("1.2.0"); # v1.2.0 |
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18 | |
19 | $perlver = version->new(5.005_03); # must not be quoted! |
20 | print $perlver; # 5.005030 |
21 | |
22 | =head1 DESCRIPTION |
23 | |
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24 | Overloaded version objects for all modern versions of Perl. This module |
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25 | implements all of the features of version objects which will be part |
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26 | of Perl 5.10.0. |
27 | |
28 | =head2 BEST PRACTICES |
29 | |
30 | If you intend for your module to be used by different releases of Perl, |
31 | and/or for your $VERSION scalar to mean what you think it means, there |
32 | are a few simple rules to follow: |
33 | |
34 | =over 4 |
35 | |
36 | =item * Be consistent |
37 | |
38 | Whichever of the two types of version objects that you choose to employ, |
39 | you should stick to either L<Numeric Versions> or L<Extended Versions> |
40 | and not mix them together. While this is I<possible>, it is very |
41 | confusing to the average user. |
42 | |
43 | If you intend to use L<Extended Versions>, you are strongly encouraged |
44 | to use the L<qv()> operator with a quoted term, e.g.: |
45 | |
46 | use version; our $VERSION = qv("1.2.3"); |
47 | |
48 | on a single line as above. |
49 | |
50 | At the very least, decide on which of the several ways to initialize |
51 | your version objects you prefer and stick with it. It is also best to |
52 | be explicit about what value you intend to assign your version object |
53 | and to not rely on hidden behavior of the parser. |
54 | |
55 | =item * Be careful |
56 | |
57 | If you are using Module::Build or ExtUtils::MakeMaker, so that you can |
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58 | release your module to CPAN, you have to recognize that neither of those |
59 | programs completely handles version objects natively (yet). If you use |
60 | version objects with Module::Build, you should add an explicit dependency |
61 | to the release of version.pm in your Build.PL: |
62 | |
63 | my $builder = Module::Build->new( |
64 | ... |
65 | requires => { |
66 | ... , |
67 | 'version' => 0.50, |
68 | ..., |
69 | }, |
70 | ... |
71 | ); |
72 | |
73 | and it should Just Work(TM). Module::Build will [hopefully soon] |
74 | include full support for version objects; there are no current plans |
75 | to patch ExtUtils::MakeMaker to support version objects. |
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76 | |
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77 | =back |
78 | |
79 | =head2 Using modules that use version.pm |
80 | |
81 | As much as possible, the version.pm module remains compatible with all |
82 | current code. However, if your module is using a module that has defined |
83 | C<$VERSION> using the version class, there are a couple of things to be |
84 | aware of. For purposes of discussion, we will assume that we have the |
85 | following module installed: |
86 | |
87 | package Example; |
88 | use version; $VERSION = qv('1.2.2'); |
89 | ...module code here... |
90 | 1; |
91 | |
92 | =over 4 |
93 | |
94 | =item Numeric versions always work |
95 | |
96 | Code of the form: |
97 | |
98 | use Example 1.002003; |
99 | |
100 | will always work correctly. The C<use> will perform an automatic |
101 | C<$VERSION> comparison using the floating point number given as the first |
102 | term after the module name (e.g. above 1.002.003). In this case, the |
103 | installed module is too old for the requested line, so you would see an |
104 | error like: |
105 | |
106 | Example version 1.002003 (v1.2.3) required--this is only version 1.002002 (v1.2.2)... |
107 | |
108 | =item Extended version work sometimes |
109 | |
110 | With Perl >= 5.6.2, you can also use a line like this: |
111 | |
112 | use Example 1.2.3; |
113 | |
114 | and it will again work (i.e. give the error message as above), even with |
115 | releases of Perl which do not normally support v-strings (see L<What about |
116 | v-strings> below). This has to do with that fact that C<use> only checks |
117 | to see if the second term I<looks like a number> and passes that to the |
118 | replacement L<UNIVERSAL::VERSION>. This is not true in Perl 5.005_04, |
119 | however, so you are B<strongly encouraged> to always use a numeric version |
120 | in your code, even for those versions of Perl which support the extended |
121 | version. |
122 | |
123 | =back |
124 | |
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125 | =head2 What IS a version |
126 | |
127 | For the purposes of this module, a version "number" is a sequence of |
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128 | positive integer values separated by one or more decimal points and |
129 | optionally a single underscore. This corresponds to what Perl itself |
130 | uses for a version, as well as extending the "version as number" that |
131 | is discussed in the various editions of the Camel book. |
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132 | |
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133 | There are actually two distinct kinds of version objects: |
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134 | |
135 | =over 4 |
136 | |
137 | =item * Numeric Versions |
138 | |
139 | Any initial parameter which "looks like a number", see L<Numeric |
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140 | Versions>. This also covers versions with a single decimal point and |
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141 | a single embedded underscore, see L<Numeric Alpha Versions>, even though |
142 | these must be quoted to preserve the underscore formatting. |
143 | |
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144 | =item * Extended Versions |
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145 | |
146 | Any initial parameter which contains more than one decimal point |
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147 | and an optional embedded underscore, see L<Extended Versions>. This |
148 | is what is commonly used in most open source software as the "external" |
149 | version (the one used as part of the tag or tarfile name). The use |
150 | of the exported L<qv()> function also produces this kind of version |
151 | object. |
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152 | |
153 | =back |
154 | |
155 | Both of these methods will produce similar version objects, in that |
156 | the default stringification will yield the version L<Normal Form> only |
157 | if required: |
158 | |
159 | $v = version->new(1.002); # 1.002, but compares like 1.2.0 |
160 | $v = version->new(1.002003); # 1.002003 |
161 | $v2 = version->new( "1.2.3"); # v1.2.3 |
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162 | |
163 | In specific, version numbers initialized as L<Numeric Versions> will |
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164 | stringify in Numeric form. Version numbers initialized as L<Extended Versions> |
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165 | will be stringified as L<Normal Form>. |
166 | |
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167 | =head2 Numeric Versions |
168 | |
169 | These correspond to historical versions of Perl itself prior to 5.6.0, |
170 | as well as all other modules which follow the Camel rules for the |
171 | $VERSION scalar. A numeric version is initialized with what looks like |
172 | a floating point number. Leading zeros B<are> significant and trailing |
173 | zeros are implied so that a minimum of three places is maintained |
174 | between subversions. What this means is that any subversion (digits |
175 | to the right of the decimal place) that contains less than three digits |
176 | will have trailing zeros added to make up the difference, but only for |
177 | purposes of comparison with other version objects. For example: |
178 | |
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179 | # Prints Equivalent to |
180 | $v = version->new( 1.2); # 1.200 v1.200.0 |
181 | $v = version->new( 1.02); # 1.020 v1.20.0 |
182 | $v = version->new( 1.002); # 1.002 v1.2.0 |
183 | $v = version->new( 1.0023); # 1.002300 v1.2.300 |
184 | $v = version->new( 1.00203); # 1.002030 v1.2.30 |
185 | $v = version->new( 1.002003); # 1.002003 v1.2.3 |
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186 | |
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187 | All of the preceding examples are true whether or not the input value is |
188 | quoted. The important feature is that the input value contains only a |
189 | single decimal. See also L<Alpha Versions> for how to handle |
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190 | |
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191 | IMPORTANT NOTE: As shown above, if your numeric version contains more |
192 | than 3 significant digits after the decimal place, it will be split on |
193 | each multiple of 3, so 1.0003 is equivalent to v1.0.300, due to the need |
194 | to remain compatible with Perl's own 5.005_03 == 5.5.30 interpretation. |
195 | Any trailing zeros are ignored for mathematical comparison purposes. |
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196 | |
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197 | =head2 Extended Versions |
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198 | |
199 | These are the newest form of versions, and correspond to Perl's own |
200 | version style beginning with 5.6.0. Starting with Perl 5.10.0, |
201 | and most likely Perl 6, this is likely to be the preferred form. This |
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202 | method normally requires that the input parameter be quoted, although |
203 | Perl's after 5.8.1 can use v-strings as a special form of quoting, but |
204 | this is highly discouraged. |
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205 | |
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206 | Unlike L<Numeric Versions>, Extended Versions have more than |
207 | a single decimal point, e.g.: |
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208 | |
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209 | # Prints |
210 | $v = version->new( "v1.200"); # v1.200.0 |
211 | $v = version->new("v1.20.0"); # v1.20.0 |
212 | $v = qv("v1.2.3); # v1.2.3 |
213 | $v = qv("1.2.3"); # v1.2.3 |
214 | $v = qv("1.20"); # v1.20.0 |
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215 | |
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216 | In general, Extended Versions permit the greatest amount of freedom |
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217 | to specify a version, whereas Numeric Versions enforce a certain |
218 | uniformity. See also L<New Operator> for an additional method of |
219 | initializing version objects. |
220 | |
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221 | Just like L<Numeric Versions>, Extended Versions can be used as |
222 | L<Alpha Versions>. |
223 | |
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224 | =head2 Numeric Alpha Versions |
225 | |
226 | The one time that a numeric version must be quoted is when a alpha form is |
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227 | used with an otherwise numeric version (i.e. a single decimal point). This |
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228 | is commonly used for CPAN releases, where CPAN or CPANPLUS will ignore alpha |
229 | versions for automatic updating purposes. Since some developers have used |
230 | only two significant decimal places for their non-alpha releases, the |
231 | version object will automatically take that into account if the initializer |
232 | is quoted. For example Module::Example was released to CPAN with the |
233 | following sequence of $VERSION's: |
234 | |
235 | # $VERSION Stringified |
236 | 0.01 0.010 |
237 | 0.02 0.020 |
238 | 0.02_01 0.02_0100 |
239 | 0.02_02 0.02_0200 |
240 | 0.03 0.030 |
241 | etc. |
242 | |
243 | As you can see, the version object created from the values in the first |
244 | column may contain a trailing 0, but will otherwise be both mathematically |
245 | equivalent and sorts alpha-numerically as would be expected. |
246 | |
247 | =head2 Object Methods |
248 | |
249 | Overloading has been used with version objects to provide a natural |
250 | interface for their use. All mathematical operations are forbidden, |
251 | since they don't make any sense for base version objects. |
252 | |
253 | =over 4 |
254 | |
255 | =item * New Operator |
256 | |
257 | Like all OO interfaces, the new() operator is used to initialize |
258 | version objects. One way to increment versions when programming is to |
259 | use the CVS variable $Revision, which is automatically incremented by |
260 | CVS every time the file is committed to the repository. |
261 | |
262 | In order to facilitate this feature, the following |
263 | code can be employed: |
264 | |
265 | $VERSION = version->new(qw$Revision: 2.7 $); |
266 | |
267 | and the version object will be created as if the following code |
268 | were used: |
269 | |
270 | $VERSION = version->new("v2.7"); |
271 | |
272 | In other words, the version will be automatically parsed out of the |
273 | string, and it will be quoted to preserve the meaning CVS normally |
274 | carries for versions. The CVS $Revision$ increments differently from |
275 | numeric versions (i.e. 1.10 follows 1.9), so it must be handled as if |
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276 | it were a L<Extended Version>. |
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277 | |
278 | A new version object can be created as a copy of an existing version |
279 | object, either as a class method: |
280 | |
281 | $v1 = version->new(12.3); |
282 | $v2 = version->new($v1); |
283 | |
284 | or as an object method: |
285 | |
286 | $v1 = version->new(12.3); |
287 | $v2 = $v1->new(); |
288 | |
289 | and in each case, $v1 and $v2 will be identical. |
290 | |
291 | =back |
292 | |
293 | =over 4 |
294 | |
295 | =item * qv() |
296 | |
297 | An alternate way to create a new version object is through the exported |
298 | qv() sub. This is not strictly like other q? operators (like qq, qw), |
299 | in that the only delimiters supported are parentheses (or spaces). It is |
300 | the best way to initialize a short version without triggering the floating |
301 | point interpretation. For example: |
302 | |
303 | $v1 = qv(1.2); # 1.2.0 |
304 | $v2 = qv("1.2"); # also 1.2.0 |
305 | |
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306 | As you can see, either a bare number or a quoted string can usually |
307 | be used interchangably, except in the case of a trailing zero, which |
308 | must be quoted to be converted properly. For this reason, it is strongly |
309 | recommended that all initializers to qv() be quoted strings instead of |
310 | bare numbers. |
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311 | |
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312 | To prevent the C<qv()> function from being exported to the caller's namespace, |
313 | either use version with a null parameter: |
314 | |
315 | use version (); |
316 | |
317 | or just require version, like this: |
318 | |
319 | require version; |
320 | |
321 | Both methods will prevent the import() method from firing and exporting the |
322 | C<qv()> sub. This is true of subclasses of version as well, see |
323 | L<SUBCLASSING> for details. |
324 | |
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325 | =back |
326 | |
327 | For the subsequent examples, the following three objects will be used: |
328 | |
329 | $ver = version->new("1.2.3.4"); # see "Quoting" below |
330 | $alpha = version->new("1.2.3_4"); # see "Alpha versions" below |
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331 | $nver = version->new(1.002); # see "Numeric Versions" above |
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332 | |
333 | =over 4 |
334 | |
335 | =item * Normal Form |
336 | |
337 | For any version object which is initialized with multiple decimal |
338 | places (either quoted or if possible v-string), or initialized using |
339 | the L<qv()> operator, the stringified representation is returned in |
340 | a normalized or reduced form (no extraneous zeros), and with a leading 'v': |
341 | |
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342 | print $ver->normal; # prints as v1.2.3.4 |
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343 | print $ver->stringify; # ditto |
344 | print $ver; # ditto |
345 | print $nver->normal; # prints as v1.2.0 |
346 | print $nver->stringify; # prints as 1.002, see "Stringification" |
347 | |
348 | In order to preserve the meaning of the processed version, the |
349 | normalized representation will always contain at least three sub terms. |
350 | In other words, the following is guaranteed to always be true: |
351 | |
352 | my $newver = version->new($ver->stringify); |
353 | if ($newver eq $ver ) # always true |
354 | {...} |
355 | |
356 | =back |
357 | |
358 | =over 4 |
359 | |
360 | =item * Numification |
361 | |
362 | Although all mathematical operations on version objects are forbidden |
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363 | by default, it is possible to retrieve a number which corresponds |
364 | to the version object through the use of the $obj->numify |
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365 | method. For formatting purposes, when displaying a number which |
366 | corresponds a version object, all sub versions are assumed to have |
367 | three decimal places. So for example: |
368 | |
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369 | print $ver->numify; # prints 1.002003004 |
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370 | print $nver->numify; # prints 1.002 |
371 | |
372 | Unlike the stringification operator, there is never any need to append |
373 | trailing zeros to preserve the correct version value. |
374 | |
375 | =back |
376 | |
377 | =over 4 |
378 | |
379 | =item * Stringification |
380 | |
381 | In order to mirror as much as possible the existing behavior of ordinary |
382 | $VERSION scalars, the stringification operation will display differently, |
383 | depending on whether the version was initialized as a L<Numeric Version> |
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384 | or L<Extended Version>. |
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385 | |
386 | What this means in practice is that if the normal CPAN and Camel rules are |
387 | followed ($VERSION is a floating point number with no more than 3 decimal |
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388 | points), the stringified output will be exactly the same as the numified |
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389 | output. There will be no visible difference, although the internal |
390 | representation will be different, and the L<Comparison operators> will |
391 | function using the internal coding. |
392 | |
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393 | If a version object is initialized using a L<Extended Version> form, then |
394 | the stringified form will be the L<Normal Form>. The $obj->normal |
395 | operation can always be used to produce the L<Normal Form>, even if the |
396 | version was originally a L<Numeric Version>. |
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397 | |
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398 | print $ver->stringify; # prints v1.2.3.4 |
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399 | print $nver->stringify; # prints 1.002 |
400 | |
401 | =back |
402 | |
403 | =over 4 |
404 | |
405 | =item * Comparison operators |
406 | |
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407 | Both C<cmp> and C<E<lt>=E<gt>> operators perform the same comparison between |
408 | terms (upgrading to a version object automatically). Perl automatically |
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409 | generates all of the other comparison operators based on those two. |
410 | In addition to the obvious equalities listed below, appending a single |
411 | trailing 0 term does not change the value of a version for comparison |
412 | purposes. In other words "v1.2" and "1.2.0" will compare as identical. |
413 | |
414 | For example, the following relations hold: |
415 | |
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416 | As Number As String Truth Value |
417 | ------------- ---------------- ----------- |
418 | $ver > 1.0 $ver gt "1.0" true |
419 | $ver < 2.5 $ver lt true |
420 | $ver != 1.3 $ver ne "1.3" true |
421 | $ver == 1.2 $ver eq "1.2" false |
422 | $ver == 1.2.3.4 $ver eq "1.2.3.4" see discussion below |
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423 | |
424 | It is probably best to chose either the numeric notation or the string |
425 | notation and stick with it, to reduce confusion. Perl6 version objects |
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426 | B<may> only support numeric comparisons. See also L<Quoting>. |
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427 | |
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428 | WARNING: Comparing version with unequal numbers of decimal points (whether |
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429 | explicitly or implicitly initialized), may yield unexpected results at |
430 | first glance. For example, the following inequalities hold: |
431 | |
432 | version->new(0.96) > version->new(0.95); # 0.960.0 > 0.950.0 |
433 | version->new("0.96.1") < version->new(0.95); # 0.096.1 < 0.950.0 |
434 | |
435 | For this reason, it is best to use either exclusively L<Numeric Versions> or |
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436 | L<Extended Versions> with multiple decimal points. |
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437 | |
438 | =back |
439 | |
440 | =over 4 |
441 | |
442 | =item * Logical Operators |
443 | |
444 | If you need to test whether a version object |
445 | has been initialized, you can simply test it directly: |
446 | |
447 | $vobj = version->new($something); |
448 | if ( $vobj ) # true only if $something was non-blank |
449 | |
450 | You can also test whether a version object is an L<Alpha version>, for |
451 | example to prevent the use of some feature not present in the main |
452 | release: |
453 | |
454 | $vobj = version->new("1.2_3"); # MUST QUOTE |
455 | ...later... |
456 | if ( $vobj->is_alpha ) # True |
457 | |
458 | =back |
459 | |
460 | =head2 Quoting |
461 | |
462 | Because of the nature of the Perl parsing and tokenizing routines, |
463 | certain initialization values B<must> be quoted in order to correctly |
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464 | parse as the intended version, especially when using the L<qv()> operator. |
465 | In all cases, a floating point number passed to version->new() will be |
466 | identically converted whether or not the value itself is quoted. This is |
467 | not true for L<qv()>, however, when trailing zeros would be stripped on |
468 | an unquoted input, which would result in a very different version object. |
469 | |
470 | In addition, in order to be compatible with earlier Perl version styles, |
471 | any use of versions of the form 5.006001 will be translated as v5.6.1. |
472 | In other words, a version with a single decimal point will be parsed as |
473 | implicitly having three digits between subversions, but only for internal |
474 | comparison purposes. |
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475 | |
476 | The complicating factor is that in bare numbers (i.e. unquoted), the |
477 | underscore is a legal numeric character and is automatically stripped |
478 | by the Perl tokenizer before the version code is called. However, if |
479 | a number containing one or more decimals and an underscore is quoted, i.e. |
480 | not bare, that is considered a L<Alpha Version> and the underscore is |
481 | significant. |
482 | |
483 | If you use a mathematic formula that resolves to a floating point number, |
484 | you are dependent on Perl's conversion routines to yield the version you |
485 | expect. You are pretty safe by dividing by a power of 10, for example, |
486 | but other operations are not likely to be what you intend. For example: |
487 | |
488 | $VERSION = version->new((qw$Revision: 1.4)[1]/10); |
489 | print $VERSION; # yields 0.14 |
490 | $V2 = version->new(100/9); # Integer overflow in decimal number |
491 | print $V2; # yields something like 11.111.111.100 |
492 | |
493 | Perl 5.8.1 and beyond will be able to automatically quote v-strings but |
494 | that is not possible in earlier versions of Perl. In other words: |
495 | |
496 | $version = version->new("v2.5.4"); # legal in all versions of Perl |
497 | $newvers = version->new(v2.5.4); # legal only in Perl >= 5.8.1 |
498 | |
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499 | =head2 What about v-strings? |
500 | |
501 | Beginning with Perl 5.6.0, an alternate method to code arbitrary strings |
502 | of bytes was introduced, called v-strings. They were intended to be an |
503 | easy way to enter, for example, Unicode strings (which contain two bytes |
504 | per character). Some programs have used them to encode printer control |
505 | characters (e.g. CRLF). They were also intended to be used for $VERSION, |
506 | but their use as such has been problematic from the start. |
507 | |
508 | There are two ways to enter v-strings: a bare number with two or more |
509 | decimal points, or a bare number with one or more decimal points and a |
510 | leading 'v' character (also bare). For example: |
511 | |
512 | $vs1 = 1.2.3; # encoded as \1\2\3 |
513 | $vs2 = v1.2; # encoded as \1\2 |
514 | |
515 | However, the use of v-strings to initialize version objects with this |
516 | module is only possible with Perl 5.8.1 or better (which contain special |
517 | code to enable it). Their use is B<strongly> discouraged in all |
518 | circumstances (especially the leading 'v' style), since the meaning will |
519 | change depending on which Perl you are running. It is better to directly |
520 | use L<"Extended Versions"> to ensure the proper interpretation. |
521 | |
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522 | |
523 | =head2 Types of Versions Objects |
524 | |
525 | There are two types of Version Objects: |
526 | |
527 | =over 4 |
528 | |
529 | =item * Ordinary versions |
530 | |
531 | These are the versions that normal modules will use. Can contain as |
532 | many subversions as required. In particular, those using RCS/CVS can |
533 | use the following: |
534 | |
535 | $VERSION = version->new(qw$Revision: 2.7 $); |
536 | |
537 | and the current RCS Revision for that file will be inserted |
538 | automatically. If the file has been moved to a branch, the Revision |
539 | will have three or more elements; otherwise, it will have only two. |
540 | This allows you to automatically increment your module version by |
541 | using the Revision number from the primary file in a distribution, see |
542 | L<ExtUtils::MakeMaker/"VERSION_FROM">. |
543 | |
544 | =item * Alpha Versions |
545 | |
546 | For module authors using CPAN, the convention has been to note |
547 | unstable releases with an underscore in the version string, see |
548 | L<CPAN>. Alpha releases will test as being newer than the more recent |
549 | stable release, and less than the next stable release. For example: |
550 | |
551 | $alphaver = version->new("12.03_01"); # must be quoted |
552 | |
553 | obeys the relationship |
554 | |
555 | 12.03 < $alphaver < 12.04 |
556 | |
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557 | Alpha versions with a single decimal point will be treated exactly as if |
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558 | they were L<Numeric Versions>, for parsing purposes. The stringification for |
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559 | alpha versions with a single decimal point may seem surprising, since any |
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560 | trailing zeros will visible. For example, the above $alphaver will print as |
561 | |
562 | 12.03_0100 |
563 | |
564 | which is mathematically equivalent and ASCII sorts exactly the same as |
565 | without the trailing zeros. |
566 | |
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567 | Alpha versions with more than a single decimal point will be treated |
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568 | exactly as if they were L<Extended Versions>, and will display without any |
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569 | trailing (or leading) zeros, in the L<Version Normal> form. For example, |
570 | |
571 | $newver = version->new("12.3.1_1"); |
572 | print $newver; # v12.3.1_1 |
573 | |
574 | =head2 Replacement UNIVERSAL::VERSION |
575 | |
576 | In addition to the version objects, this modules also replaces the core |
577 | UNIVERSAL::VERSION function with one that uses version objects for its |
578 | comparisons. The return from this operator is always the numified form, |
579 | and the warning message generated includes both the numified and normal |
580 | forms (for clarity). |
581 | |
582 | For example: |
583 | |
584 | package Foo; |
585 | $VERSION = 1.2; |
586 | |
587 | package Bar; |
588 | $VERSION = "1.3.5"; # works with all Perl's (since it is quoted) |
589 | |
590 | package main; |
591 | use version; |
592 | |
593 | print $Foo::VERSION; # prints 1.2 |
594 | |
595 | print $Bar::VERSION; # prints 1.003005 |
596 | |
597 | eval "use CGI 10"; # some far future release |
598 | print $@; # prints "CGI version 10 (10.0.0) required..." |
599 | |
600 | IMPORTANT NOTE: This may mean that code which searches for a specific |
601 | string (to determine whether a given module is available) may need to be |
602 | changed. |
603 | |
604 | The replacement UNIVERSAL::VERSION, when used as a function, like this: |
605 | |
606 | print $module->VERSION; |
607 | |
608 | will also exclusively return the numified form. Technically, the |
609 | $module->VERSION function returns a string (PV) that can be converted to a |
610 | number following the normal Perl rules, when used in a numeric context. |
611 | |
612 | =head1 SUBCLASSING |
613 | |
614 | This module is specifically designed and tested to be easily subclassed. |
615 | In practice, you only need to override the methods you want to change, but |
616 | you have to take some care when overriding new() (since that is where all |
617 | of the parsing takes place). For example, this is a perfect acceptable |
618 | derived class: |
619 | |
620 | package myversion; |
621 | use base version; |
622 | sub new { |
623 | my($self,$n)=@_; |
624 | my $obj; |
625 | # perform any special input handling here |
626 | $obj = $self->SUPER::new($n); |
627 | # and/or add additional hash elements here |
628 | return $obj; |
629 | } |
630 | |
631 | See also L<version::AlphaBeta> on CPAN for an alternate representation of |
632 | version strings. |
633 | |
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634 | B<NOTE:> Although the L<qv> operator is not a true class method, but rather a |
635 | function exported into the caller's namespace, a subclass of version will |
636 | inherit an import() function which will perform the correct magic on behalf |
637 | of the subclass. |
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638 | |
639 | =head1 EXPORT |
640 | |
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641 | qv - Extended Version initialization operator |
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642 | |
643 | =head1 AUTHOR |
644 | |
645 | John Peacock E<lt>jpeacock@cpan.orgE<gt> |
646 | |
647 | =head1 SEE ALSO |
648 | |
649 | L<perl>. |
650 | |
651 | =cut |